Russia's security chief said on Tuesday that NATO expansion posed "quite a serious threat" to the country.

"We have strong doubts that NATO enlargement will help us feel more secure. The alliance poses quite a serious threat to us," Russian Security Council Secretary Nikolai Patrushev was quoted as saying by Russian news agencies.

NATO leaders had promised not to admit new members, but the bloc's members states have increased from 12 to 28, including former Warsaw Pact countries and ex-Soviet republics, Patrushev said.

He also accused NATO of absorbing Georgia and Ukraine into the military alliance. "Referendums have showed that Ukraine has not striven for NATO membership, at least for now," he said.

A new Russian military doctrine approved by President Dmitry Medvedev last Friday defines NATO expansion as a threat.

NATO Secretary General Anders Fogh Rasmussen, on the sidelines of a security conference in Munich last week, said the doctrine did not reflect realities and contradicted NATO endeavors to improve ties with Russia.